Astronomical discovery that moves: our cosmic address has changed!

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The Shapley Concentration, the supercluster where we live.

The Shapley Concentration, the supercluster where we live.

© Valade & al, Nature 2024

In 2014, Hélène Courtois, Daniel PomaredeRB Tully and others make a resounding announcement: they have identified that the Milky Way is gravitationally linked to 100,000 other galaxies spanning 500 million light years. Part of their 10 years of observations having been made at Mauna Kea, in Hawaii, they gave the very poetic name of Laniakea to this cosmic ensemble to which we belong.

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Laniakea and the cosmic filaments made up of galaxies and their speeds. The red dot represents our position: *“We are here.”

Laniakea and the cosmic filaments made up of galaxies and their speeds. The red dot represents our position: *“We are here.”

© Courtois, Tully, Pomarède & al (Nature)

Laniakea means “immeasurable paradise” and immeasurable means “which cannot be measured”. A shame, because these scientists have spent a decade measuring the speeds and directions of all these galaxies. In this, Hélène Courtois and Daniel Pomarède followed to the letter the recommendation of Galileo to measure everything that can be measured and make measurable what is not.

Astronomy has the power to greatly reduce the size of our problems…

They also honored astronomy, as well as the illustrious Carl Sagan who saw in this science the means for human beings to know their place in the Universe. Thanks to Laniakea, we knew a little more where and what we are. We can now take a dizzying perspective on our existence. Humanity is this little pile of carbon and oxygen atoms on a little blue planet in a little galaxy carried away in a flood of other galaxies.

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The different structures to which we belong.

The different structures to which we belong.

© Andrew Z. Colvin

The galactic superclusters neighboring ours (Virgo supercluster), notably the Serpentarius supercluster (Ophiuchus), in yellow, towards which we are heading.

The galactic superclusters neighboring ours (Virgo supercluster), notably the Serpentarius supercluster (Ophiuchus), in yellow, towards which we are heading.

© Andrew Z. Colvin

Yes, but now our address has changed. Or rather, today we can probably add a line to our planetary calling card, because we exist in an even larger supercluster. This first-hand information was made by almost the same team as that of Laniakea. Let’s summarize…

Humanity lives on Earth, in the Solar System, in the Orion Arm, in the Milky Way, in the Virgo Cluster, in the Virgo Supercluster, in Laniakea and in the Shapley Concentration.

The gravitational currents that connect galaxy clusters. And what's more, it's magnificent.

The gravitational currents that connect galaxy clusters. And what's more, it's magnificent.

© Valade & al, Nature 2024

The “watershed” technique

It was necessary to study 38,000 groups of galaxies and 56,000 galaxies to determine this new gravitational affiliation. This is the Cosmic Flows 4 program. The parts furthest from us, due to the expansion of the Universe, are carried away by a speed of around 30,000 km/s! However, indirectly, we are still connected to them.

Space is distorted by the masses found there and the concentration of the latter. Think about the formula of John Wheelercollaborator ofEinstein : “Matter tells space how to bend and space tells matter how to move forward.” Groups of galaxies therefore slide towards each other at speeds of hundreds of kilometers per second. So, “the 'Local Cluster' consisting of the Milky Way and Andromeda is speeding at 630 km/s towards the Centaurus cluster, and these streamlines then direct us towards the cluster located in the constellation Ophiuchus-Serpentaris”as Daniel Pomarède, one of the authors of this article published on Nature.

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On the left, the Great Sloan Wall, 1.35 billion light years across.

On the left, the Great Sloan Wall, 1.35 billion light years across.

© Valade & al, Nature 2024

This new volume is approximately 10 times greater than that of Laniakea, but it remains much smaller than the largest gravitational structure known in the Universe, the Great Sloan Wall, also made up of galaxies in clusters and which extends over almost 1 .5 billion light years!

When we expand the Universe

It should be noted that our supercluster still seems to be attracted towards another superstructure, but that is another story, leading to other discoveries. Let's already savor this one and think back that 500 years ago, for 99% of Humanity, the World – the Universe – was limited to the Earth. Then thanks to Galileo and the astronomical telescope, it expanded to the Solar System and beyond, then the Universe became the Milky Way.

Just 100 years ago, astronomers gathered in a Great Debate discovered the unimaginable: there existed thousands, millions, then billions of other galaxies. On this day in 1924, the Universe expanded like never before in the minds of Men. Hey, one of the debaters was called Harlow Shapley

As a gift, here is an animated video of a story of the creation of the world according to a Hawaiian legend:

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